Winter

1
Kuroshio Extension Front Has Strong Seasonal
Impacts on Clouds
Hiroki Tokinaga1, Youichi Tanimoto2,3, Shang-Ping
Xie1, Takeaki Sampe1, Hiroyuki Tomita4, Hiroshi
Ichikawa4 1IPRC, 2Hokkaido Univ., 3FRCGC/JAMSTEC,
4IORGC/JAMSTEC
Winter
Summer
Air-sea temp. difference
(e)
(a)
(b)
Frequency of sea fog
(f)
(d)
(c)
(e) Air-sea temperature difference and (f)
sea-fog frequency under the southerly winds in
June. Dashed line is 0ºC contour of air-sea temp.
difference.
(a) Surface heat flux, (b) cloud liquid water,
(c) high-pass filtered SLP, and (d) cloud top
occurrence between 500-700hPa in
December-February. Contours are SST at 2ºC
intervals.
In summer, sea fog frequently occurs on the
northern flank of the KE front and subarctic
fronts under southerly warm advection that
suppresses surface heat flux and stabilizes the
surface atmosphere (Fig. f). Sea fog is
infrequently observed over the KE front even
under southerly conditions because the warm ocean
current weakens atmospheric stratification and
promotes vertical mixing (Fig. e).
In winter, intense turbulent heat release from
the ocean takes place on the southern flank of
the Kuroshio Extension (KE) front (Fig. a), where
cloud liquid water shows a local maximum and the
cloud top penetrates above the marine atmospheric
boundary layer (MABL) and reaches the
mid-troposphere (Fig. d). Our results suggest a
sea level pressure mechanism, where temperature
gradient in the MABL induces strong surface wind
convergence on the southern flank of the KE
front, deepening the clouds there (Fig. c).